If a heated steel nail were placed in pure o2, would you expect it to burn as readily as the steel wool does?

No, the reaction would not be as vigorous as the steel wool because of the surface area. When steel wool comes in contact with pure oxygen, the rapid reaction takes place due to a large increase in surface area. On the contrary, the steel nail has a lesser surface area and the reaction with oxygen would be slow.

bcde is the incorrect answer it is a

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.